Method of dissolving orthotitanic acid



United States Patent METHOD OF DISSOLVING ORTHOTITANIC ACID No Drawing. Application June 21, 1955 Serial No. 517,043

Claims priority, application France July 2, 1954 2 Claims. (Cl. 2387) My invention has for its object improvements in the method for producing titanium oxide by treating sodium titanate with a mineral acid so as to obtain a solution of a titanium salt, which solution is then hydrolyzed at a raised temperature in order to produce a precipitate of very pure white titanium oxide TiO the magnitude of the particles forming which ranges between 0.5 and 1 micron.

The sodium titanate referred to is the product obtained in accordance with the method disclosed in my copending application Ser. No. 517,044, now abandoned, filed this day and entitled Improvements in the Treatment of Titanium Bearing Substances. The sodium titanate prepared through this method is formed almost entirely by the pure compound Na TiO and it is a well known fact that this titanate shows the property of being almost completely destroyed hydrolytically to form its two component oxides through a succession of water washing steps as shown diagrammatically by the equation Na TiO 3 nHzo Na O enters the solution in the form of soda (ZNaOH) and there remain precipitated floccules of titanic acid.

According to my invention, 1 provide exclusively through the hydrolytic destruction of this titanate orthotitanic acid (TiO 2H O) which is obtained only through washing in cold water i.e. water the temperature of which is below 40 C.

If a washing with hot or boiling water had been performed, the titanic acid released as obtained through the action of water on sodium titanate would be metatitanic acid TiO H O which is an undesirable product for the subsequent operations to be executed. These washings made with cold water have also for their object to remove the impurities in the titanate such as chromates, vanadates etc.

It is also a well known fact that only orthotitanic acid can be dissolved by diluted mineral acids. The dissolution of this orthotitanic acid may be executed by means of diluted sulfuric or hydrochloric acid.

An important feature of my improved method consists in resorting to an acid concentration such that only the orthotitanic acid is dissolved. In practice, if the titanium bearing material is produced by the sintering of ilmenite, there is a large proportion of iron oxide present in the mixture. Starting from a concentration above 40% of sulfuric acid for instance, the titanium is dissolved before the iron whereas the iron dissolves before the titanium in the opposite case of acid concentrations lower than 40%. If the titanium bearing material is obtained through the sintering of rutile, the amount of iron oxide in the mixture is much less, but in such a case I have found that when resorting to acid having a concentration less than 40%, the dissolution of the titanium is much lower.

Furthermore, this dissolution producing titanium salts such as the sulfate or the chloride is generally incomplete, the speed of reaction decrease rapidly and leads to an equilibrium between the components, to wit the titanium salt, the mineral acid and the orthotitanic acid.

My invention consists chiefly in incorporating into the orthotitanic acid which it is desired to render soluble a small amount of a reaction accelerator. I have found according to the main feature of my invention that it is possible for this purpose to resort with remarkable results to alkaline metal halides and in particular to sodium chloride and sodium fluoride.

Amounts ranging between 0.5 and 5% of such accelerator substances have been found sufficient.

We have obtained the best yields (97 to 98%) by resorting to a mineral acid at a concentration of about 50% such as sulfuric acid containing 50% of the monohydrate H 30 (specific weight: 1.4 or 41 B.) while the amount of acid corresponds to 5.3 parts by weight of sulphuric acid at a concentration of 50% for 1 part of TiO;, (i.e. 2.6 parts of sulfuric acid at 98%).

The reaction is performed at raised temperature and is ended in 20 to 30 minutes.

By way of example and as an illustration of the preceding disclosure, 1 may admix:

100 parts by weight of orthotitanic acid corresponding to 69 parts of TiO 366 parts by weight of sulfuric acid at a concentration of 50%.

2.8 parts of sodium fluoride.

The mixture is heated during 25 minutes at a temperature near boiling point. The solution obtained is then cooled, filtered or submitted to centrifugation so as to produce a clear solution of titanium sulfate.

This solution also contains a small amount of iron which has been dissolved in the form of iron sulfate.

Numerous methods for hydrolyzing solutions of titanium sulfate or chloride are known.

According to a preferred embodiment of my invention I provide for the hydrolyzing of a solution of a titanous salt. The sulfuric solution obtained precedingly is reduced by hydrogen in statu nascendi as obtained through the heating of said solution in the vicinity of its boiling point in the presence of iron scrap. It is a well known fact that taking as a reducer such hydrogen in statu nascendi only salts of titanous oxide admixed with titanic oxide. This compound oxide has approximately the formula 2TiO TiO and appears as the blue oxide form. The reduction may thus be prosecuted to its end without any risk of obtaining other oxides. After a comparatively short time, say 15 minutes, it is possible to produce in this manner a minimum of of titanous sulfate the composition of which varies with the proportion of titanium oxide associated with the sulfuric anhydride in the salt; the solution appears as a comparatively viscid liquid of a bluish black color. This solution which is first heated to a temperature of 80 C. is simply poured at a slow rate into a predetermined volume of boiling water and it has been found that this titanous sulfate is hydrolyzed and produces on one hand sulfuric acid and on the other hand titanous oxide Ti O in the form of a blue precipitate.

Under the action of the stirring, of the heating and of the turbulent boiling, the major part of the precipitated Ti O is transformed into very fine white TiO the particle size of which is uniform (as an average 0.8 micron).

The uniformity of the precipitate of TiO is obtained through the systematic transformation of 1 molecule of Ti O into three molecules of TiO (Ti O +0- 3TiO This hydrolysis is performed without any seeding as is generally required when solutions of titanic sulfate are subjected to hydrolysis.

This hydrolysis is comparatively rapid since of the TiO present'in the solution is precipitated in two hours and thirty minutes.

It should be remarked that the presence of titanous salts prevents any absorption of iron through the precipitate so that at the moment of the subsequent filtering and washing with water of the paste obtained, the iron is completely removed in the form of ferrous sulfate.

The paste produced, when dried and baked, forms a pure very white .titanium oxide and if the paste contains still some blue Ti O the baking would completely transform said titanous oxide Ti O remaining in the mixture into titanic oxide T 1:02.

It it is desired to bestow pigmental properties to the titanium oxide, it is necessary to incorporate suitable additions at the moment of its baking.

What I claim is:

1. Method of dissolving orthotitanie acid which comprises heating a mixture of orthotitanic acid and an aqueous solution of an acid selected from the group consisting of sulfuric acid and hydrochloric acid, the concentration of the acid in said solution being at least 40%, in the presence of an alkali metal halide in an amount of about 0.5 to 5% by weight of the mixture.

2. Method of dissoving orthotitanic acid which comaqueous solution of an acid selected from the group consisting of sulfuric acid and hydrochloric acid, the concentration of the acid in said solution being at least 40%, in the presence of sodium fluoride in an amount of about 0.5 to 5% by weight of the mixture.

References Cited in the file of this patent UNITED STATES PATENTS 1,106,409 Rossi et a1 Aug. 11, 1914 1,731,364 Von Bichowsky Oct. 15, 1929 1,849,153 Raspe Mar. 15, 1932 1,932,087 Richter Oct. 24, 1933 2,034,923 Schmidt Mar. 24, 1936 2,098,278 Dahlstrom et al. Nov. 9, 1937 2,345,985 McKinney Apr. 4, 1944 2,433,597 Cauwenberg et al. L Dec. 30, 1947 2,494,492 Ross et al J an. 10, 1950 2,564,365 Kingsbury Aug. 14, 1951 OTHER REFERENCES I. Barksdales Titanium, page 64, Ronald Press Co., New York, NY.

Thornton: Titanium, pp. 50, 66-67, published by prises heating a mixture of orthotitanic acid and an Chemcatalog New York, 1927- 

1. METHOD OF DISSOLVING ORTHOTITANIC ACID WHICH COMPRISES HEATING A MIXTURE OF ORTHOTITANIC ACID AND AN AQUEOUS SOLUTION OF AN ACID SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID AND HYDROCHLORIC ACID, THE CONCENTRATION OF THE ACID IN SAID SOLUTION BEING AT LEAST 40%, IN THE PRESENCE OF AN ALKALI METAL HALIDE IN AN AMOUNT OF ABOUT 0.5 TO 5% BY WEIGHT OF THE MIXTURE. 